Bone anchoring device

ABSTRACT

A bone anchoring device includes an anchoring element having a head, a receiving portion having a first region adjacent to a second end for receiving the head and a recess which is open towards a first end to form two free legs for receiving a rod. The anchoring device further includes a pressure element configured to couple to the head, a first closure element and a second closure element. The first closure element cooperates with the legs to simultaneously fix the rod in the recess and fix the head in the receiving portion, and the second closure element cooperates with the legs, the second closure element acts on the pressure element and on the rod to independently fix the head in the receiving portion and fix the rod in the recess. The first closure element and the second closure element are interchangeable.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of application Ser. No. 11/484,180filed Jul. 10, 2006, which claims the benefit of U.S. ProvisionalApplication Ser. No. 60/698,885, filed Jul. 12, 2005, and claimspriority from European Patent Application EP05015138, filed Jul. 12,2005, the disclosures of which are incorporated herein by reference.

BACKGROUND

The present disclosure generally relates to devices used in bonesurgery, and more particularly, relates to a bone anchoring device.

U.S. Pat. No. 5,443,467 discloses a bone screw comprising a receivermember and a screw member having a threaded portion and a head. Apressure disk is slidable within the receiver member and acts onto thehead. The rod is placed on top of the pressure disk and the arrangementis locked by means of a rod locking nut and a lock nut exerting pressureonto the rod which then exerts pressure on the pressure disk, thuslocking the head.

U.S. Pat. No. 6,063,090 discloses a spinal fixation system with apedicle screw and a retainer head to connect the pedicle screw with alongitudinal support. An insert is provided with exerts a pressure ontothe head of the pedicle screw which is accommodated in the retainerhead. Tension means are provided to press onto the insert to lock thehead of the pedicle screw in its polyaxial position and to fix thelongitudinal support. Depending on the insert and the tension means therod and the head of the bone screw may be separately fastened.

US 2003/0100896 A1 discloses an element with a shank and a holdingelement connected to the shank for connecting to a rod. The holdingelement has a recess having a U-shaped cross-section for receiving therod with two open legs and an inner thread on the open legs and alocking element with an outer thread which cooperates with the innerthread of the legs. In one embodiment, the holding element ispolyaxially connected with the head of a bone screw. To lock the head inits polyaxial position a pressure disk is provided which acts on thehead when pressure is exerted onto the rod by means of an inner screw.In another embodiment the head can be locked independently from thefixation of the rod. If the two types of anchoring devices are to beused simultaneously during surgery it is necessary to have the differenttypes of anchoring devices separately on stock or to pre-assemble thepreferred anchoring device with the required pressure disk and/or thepressure element before or during surgery.

US 2004/0186473 discloses a bone anchoring device with a bone anchoringelement which is polyaxially connected to a receiving portion and apressure element to exert pressure onto the head to lock the head in itsposition wherein an inner screw is provided which can be screwed in thereceiving portion to exert a pressure on the rod. The inner thread endsabove the rod when the rod is inserted and an undercut is provided toallow a design of the receiving portion to be smaller in its dimensions.

In view of the above, there is a need for a bone anchoring device thatcan remedy one or more of the above described problems associated withcurrent bone anchoring devices.

SUMMARY

According to one or more embodiments of the present disclosure, a boneanchoring device is provided that is versatile in use and compact insize. The bone anchoring device according to one or more embodiments ofthe present disclosure can be used with the choice of a closure elementin two ways. If a single part closure element is selected, it ispossible to simultaneously lock the head in its polyaxial position andto fix the rod. If a two part closure element is selected, it ispossible to separately lock the head and to fix the rod. For bothapplications only one single receiving portion and pressure element isnecessary. Therefore, the surgeon can use one bone anchoring device andcan select during surgery which kind of closure mechanism shall be used.

The bone anchoring device according to one or more embodiments of thepresent disclosure is compact in size, since it is not necessary to usean outer nut or ring to prevent splaying of the legs. Also, the wallthickness of the receiving portion is such that there are no thinnedinner portions like thread runouts or undercuts that would weaken thestructure.

Further features and advantages of the disclosure will become apparentfrom the description of embodiments in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of the bone anchoring devicewith a single part closure element.

FIG. 2 shows a cross-sectional view of the bone anchoring deviceaccording to FIG. 1.

FIG. 3 shows a perspective view of the bone anchoring device of FIG. 1.

FIG. 4 shows a cross-sectional view of a bone anchoring device with atwo part closure element.

FIG. 5 shows a perspective view of the bone anchoring device of FIG. 4.

FIG. 6 shows possibilities of use of the bone anchoring device with asingle part closure element and a two part closure element.

FIG. 7 a shows in a schematic way the locking mechanism of the boneanchoring device with the single part closure element.

FIG. 7 b shows in a schematic manner the locking mechanism of the twopart closure mechanism.

DETAILED DESCRIPTION

As shown in FIGS. 1 to 3 a first embodiment of the bone anchoring deviceof the present disclosure includes a bone screw 1 having a shank 2 witha bone thread and a spherical segment-shaped head 3 which has a recess 4for engagement with a screwing-in tool. The bone anchoring devicefurther includes a receiving portion 5, which is substantiallycylindrical and has a first end 6 and a second end 7 opposite to thefirst end 6. The two ends 6, 7 are perpendicular to a longitudinal axis8. Coaxially with the longitudinal axis 8, a first bore 9 is providedwhich extends from the first end 6 to a predetermined distance from thesecond end 7. At the second end 7, an opening 10 is provided thediameter of which is smaller than the diameter of the bore 9. Thecoaxial bore 9 tapers towards the opening 10. In the embodiment shown,the coaxial bore 9 tapers in form of a spherically shaped section 11.The diameter of the coaxial bore 9 can be slightly larger than thelargest diameter of the head 3, so that the bone screw 1 can be guidedthrough the bore 9 with the shank 2 extending through the opening 10 andthe head 3 resting against the spherically shaped section 11.

The receiving portion 5 further has a U-shaped recess 12 which starts atthe first end 6 and extends in the direction of the second end 7 so thatthe bottom 13 of the U-shaped recess has a distance d from the secondend 7. The width of the U-shaped recess 12 in the lateral directionperpendicular to the longitudinal axis 8 can be slightly larger than thediameter of a rod 14 which is to be received in the U-shaped recess 12.By means of the U-shaped recess 12, two free legs 15, 16 are formedending towards the first end 6. Adjacent to the first end 6, thereceiving portion comprises an inner thread 17 at the legs 15, 16. Asecond coaxial bore 18 is provided adjacent to the first end 6 which hasa diameter larger than the diameter of the first coaxial bore 9 so thata shoulder 9 a is formed at the transition from the first bore 9 to thesecond bore 18. The inner diameter of the coaxial bore 18 and the innerdiameter between opposing crests of the inner thread 17 is substantiallythe same. The thread 17 opens out into the U-shaped recess 12.Therefore, there is no thread runout and also no thread undercut. In anassembled state, when the rod 14 is inserted into the receiving portion5, the inner thread 17 ends at a position at the legs 15, 16, which isabove the upper surface of the rod 14.

The bone anchoring device also includes a pressure element 20, which hasa substantially cylindrical construction with a first end 21 and asecond end 22 opposite to the first end 21. The outer diameter of thepressure element 20 is only slightly smaller than the inner diameter ofthe first coaxial bore 9 to allow the pressure element 20 to beintroduced into the bore 9 of the receiving portion 5 and to be moved inan axial direction. Adjacent to its second end 22 which faces the head 3in an assembled state, the pressure element 20 comprises a sphericalrecess 23, the radius of which corresponds to the radius of thespherical head 3. Adjacent to its first end 21, the pressure element hasa U-shaped recess 24 which extends transversely to the longitudinal axis8. The lateral diameter of this U-shaped recess 24 is selected such thatthe rod 14, which is to be received in the receiving portion 5, can beinserted into the recess 24 and guided laterally therein. By means ofthe U-shaped recess 24, the open legs 25, 26 of the pressure element 20are formed ending towards the first end 21. The depth of the U-shapedrecess 24, as seen in the direction of the longitudinal axis 8 of thereceiving portion 5 is larger than the diameter of the rod 14 to bereceived such that the legs 25, 26 project over the rod 14 when the rod14 rests on the bottom 27 of the U-shaped recess 24. The pressureelement 20 further comprises a coaxial bore 28 to allow for accessingthe bone screw 1 with a screw driver.

As can be seen in particular from FIGS. 1 and 2, adjacent to its firstend 21, the pressure element 20 includes a circumferential projection29, the outer diameter of which is slightly smaller than the innerdiameter of the second coaxial bore 18 of the receiving portion 5 insuch a manner that the pressure element 20 can slide with thecircumferential projection 21 in the second coaxial bore 18.

The bone anchoring device further includes a closure element which inthis embodiment is a single part closure element in form of an innerscrew 30. The outer thread of the inner screw 30 cooperates with theinner thread 17 provided at the legs 15,16. At one end, the inner screw30 has a recess 31 for engagement with a screwing-in tool. At theopposite end, the inner screw 30 has a first cylindrical projection 32the diameter of which is slightly smaller than the inner diameter of thesecond coaxial bore 18 such that the cylindrical projection 32 slidesalong the inner wall of the second coaxial bore 18 when the inner screw30 is screwed-in between the legs 25,26. The first cylindricalprojection 32 tapers into a second cylindrical projection 33 having adiameter which is larger than the diameter of the rod but smaller thanthe diameter of the second bore 18 and which engages in an assembledstate as shown in FIG. 2 with a corresponding circular recess 34adjacent to the first end 21 of the pressure element 20. The lowersurface of the cylindrical projection 33 is flat.

The dimensions of the pressure element 20 relative to the head 3 of thebone screw and to the receiving portion 5 are such that in a state inwhich the bone screw is not yet locked in its final polyaxial positionrelative to the receiving portion 5, the bottom 27 of the U-shapedrecess 24 of the pressure element 20 has a distance from the second end7 of the receiving portion which is greater than the distance d shown inFIG. 1 so that it projects above the bottom 13 of the U-shaped recess 12of the receiving portion 5 as shown in FIG. 3. In this state, thepressure element 20 is slidable in the first coaxial bore 9 and with itsprojection 21 in the second coaxial bore 18 in such a way that theprojection 21 does not rest on the shoulder 9 a. The dimension of theinner screw 30 in an axial direction is such that when the inner screw30 is not yet tightened, the lower surface of the cylindrical projection33 does not touch the surface of the rod 14.

The dimension of the inner screw 30 is such that in the finallytightened state, the inner screw 30 does not exert a pressure onto thepressure element 20, i.e., the length of the cylindrical projection 33is such that there is a gap 35 between the surface of the firstcylindrical projection 32 of the inner screw and the first end 21 of thepressure element 20. The inner thread 17 of the receiving portion 5 andthe thread of the inner screw 30 is preferably a flat thread to preventsplaying of the legs 15, 16.

In use, bone screw 1 is first introduced into the receiving portion 5with the shaft 2 guided through the opening 10 until the head 3 restsagainst the spherical section 11 or the edge formed by the opening 10.Then, the pressure element 20 is introduced into the receiving portion 5such that the spherical recess 23 encompasses the upper section of thehead 3 of the bone screw. In this state, the bottom 27 of the U-shapedrecess of the pressure element 20 projects over the bottom 13 of theU-shaped recess 12 of the receiver portion 5. In this state, ananchoring assembly is provided by the head of the bone screw 1 beingpivotably held in the spherical section 11 of the receiving portionsimilar to a ball and socket joint. Next, the bone screw 1 is screwedinto the bone. Alternatively, the receiving portion 5, the bone screw 1and the pressure element 20, i.e., the anchoring assembly, can bepreassembled and be provided with means (not shown) preventing that thepressure element 20 falls out of the receiving portion 5.

Thereafter, the rod 14 is inserted into the receiving portion 5 suchthat it rests in the bottom 27 of the pressure element 20. Due to thepolyaxial connection between the bone screw 1 and the receiving portion5, the receiving portion 5 can be aligned to have the correctorientation with respect to the rod 14. Thereafter, the inner screw 30is screwed-in between the legs 15, 16 until the lower surface ofcylindrical projection 33 comes into contact with the upper surface ofthe rod 14. The inner wall of the second coaxial bore 18 of thereceiving portion 5 acts as a guiding surface for the cylindricalprojection 32 of the inner screw which prevents tilting of the innerscrew at the time of screwing-in the inner screw 30.

At the same time, the second coaxial bore 18 and the shoulder 9 a servefor alignment of the pressure element 20 relative to the receivingportion 5. Similarly, the circular recess 34 of the pressure element 20forms a guiding surface for the cylindrical projection 33 of the innerscrew 30.

As shown in FIG. 7 a, at the time of final tightening of the inner screw30, the lower surface of the inner screw 30 presses onto the rod 14which presses onto the pressure element 20. Because of the gap 35between the lower side of the cylindrical projection 33 and the firstend 21 of the pressure element 20, pressure is exerted only on the rod14, which itself exerts pressure on the head 3 via the pressure element20. Thus, head 3 and rod 14 are fixed simultaneously.

The design of the receiving portion 5 is compact, since no outersecuring ring or nut is necessary. Since the inner thread 17 does nothave a thread runout and the inner portion of the receiving portion 5does not have an undercut, the legs 15, 16 are stiffer because of anenhanced thickness towards the inside of the receiving portion 5. Thisreduces splaying of the legs 15, 16 when screwing-in the inner screw 30.Further, the pressure element 20 having the legs projecting over the rod14 can be aligned easily in the receiving portion 5.

A second embodiment of the disclosure is shown in FIGS. 4, 5 and 7 b.The bone anchoring device shown in FIGS. 4 and 5 differs from the boneanchoring device shown in FIGS. 1 to 3 and 7 a by the closure elementused. All other parts are identical and have the same reference signs,and therefore, the description thereof will be omitted.

The closure element which is part of the embodiment shown in FIGS. 4 and5 is a two part closure element consisting of a nut 40 which can bescrewed-in between the legs 15, 16 of the receiving portion 5. The nut40 has an outer thread cooperating with the inner thread 17 of the legs15, 16. This thread can be a flat thread to prevent splaying of the legs15, 16. The nut 40 is further provided with an inner thread 42. On oneend, slits 43 are provided for engagement with a screw driver. On itsside facing the receiving portion 5, the nut 40 has an annularprojection 44, the outer diameter of which is slightly smaller than theinner diameter of the second coaxial bore 18.

The closure element further comprises an inner screw or set screw 45with an outer thread cooperating with the inner thread 42 of the nut 40.The thread can be a metric thread. The inner screw 45 has a recess 46for engagement with a screwing-in tool. The dimension of the nut 40 issuch that when it is in the fully tightened state as shown in FIG. 4,the annular projection 44 presses onto the first end 21 of the pressureelement 20. The dimension of the inner screw 46 is such that it presseson the rod 14 in the fully tightened state.

In use, as in the first embodiment, first the bone screw 1 is introducedinto the receiving portion 5. Then, the pressure element 20 is insertedand is first held loosely in the receiving portion 5. Alignment of thepressure element 20 is easy because of the coaxial first bore 9 and thecoaxial second bore 18. Following this, the bone screw 1 is screwed intothe bone and the rod 14 is inserted into the U-shaped recess 12 of thereceiving portion 5, which is in alignment with the U-shaped recess 24of the pressure element 20. At the time of placing in the rod 14, thepressure element 20 is positioned such that the bottom 27 of itsU-shaped recess 24 projects over the bottom 13 of the U-shaped recess 12of the receiving portion 5. The bone screw 1, the receiving portion 5and the pressure element 20 can also be preassembled.

The nut 40 is then screwed-in with the inner screw 45 loosely screwedinto it, until the nut 40 abuts against the upper end of the legs 25, 26of the pressure element 20 and exerts a downward force on the pressureelement 20, which presses onto the screw head 3 to lock the bone screw 1in its final polyaxial position in the receiving part 5. In this state,the rod 14 is still slidable in the U-shaped recess 24 of the pressureelement 20, since the legs 25, 26 of the pressure element 20 projectover the rod 14. In addition, the rod 14 is prevented by the nut 40 fromfalling out or from tilting. Finally, the inner screw 45 is tighteneduntil it presses onto the rod 14 and fixes the same. Thus, the fixing ofthe rod 14 takes place independently of the fixing of the head 3 asshown in FIG. 7 b. As in the first embodiment, the bone anchoring deviceis compact since an outer securing element is not needed. Further, analignment of the pressure element is facilitated.

As shown in FIG. 6, during surgery, a surgeon can select whether asingle part closure element 30 or a two part closure element 40, 45 isto be used in conjunction with the same bone anchoring device. Forcertain applications, a single part closure element with simultaneouslocking of the head 3 and fixation of the rod 14 may be advantageous inparticular if the fixation has to take place rapidly. For certain otherapplications, it may be advantageous to have the separate fixation ofthe head 3 and the rod 14. Since the surgeon can use the same boneanchoring device and is free to select the desired closure element, itis not necessary to have different receiving portions with differentpressure elements or different bone anchoring devices available.

Modifications of the embodiments of the present bone anchoring deviceare possible. Instead of a flat thread, other thread forms can be used.This may require an additional outer securing element (not shown), suchas a ring or a nut cooperating with an outer thread of the legs. It isalso conceivable to omit the inner thread and instead use a cap (notshown) with a securing pin (not shown) pressing onto the rod 14. In thiscase, the pin should be shaped such that it does not press onto thefirst end 21 of the pressure element 20 when it touches the rod 14.

The spherically-shaped section 11 of the receiving portion 5 againstwhich the head 3 rests needs not to be spherically shaped, but can haveany other shape as long as the head 3 is held by the edge of the opening10 like a ball and socket joint.

Further modifications are possible. In the second embodiment, the nut 40may have an additional cap portion (not shown) at its end facing awayfrom the cylindrical projection 44 to eliminate any danger of splayingof the legs 15, 16. In addition, modifications similar to that of thefirst embodiment are conceivable. In a further modification, thereceiving portion 5 is designed so as to allow the introduction of thehead 3 from the bottom of the receiving portion 5, that is, from thesecond end.

While a particular form of the disclosure has been illustrated anddescribed, it will be apparent that various modifications can be madewithout departing from the spirit and scope of the disclosure.Accordingly, it is not intended that the disclosure be limited, exceptas by the appended claims.

What is claimed is:
 1. A bone anchoring device comprising: an anchoringelement comprising a shank to be anchored to a bone or a vertebra and ahead; a rod; a receiving portion comprising a first end and a second endopposite to the first end, a longitudinal axis passing through the twoends, a bore coaxial with the longitudinal axis, a first region adjacentto the second end for receiving said head and a recess which is openedtowards the first end and which forms two free legs for receiving therod; a pressure element to exert a pressure on said head to lock saidhead in the receiving portion, wherein said pressure element has a firstend and a second end opposite to the first end and a U-shaped recesswhich is open towards the first end to receive the rod, the depth of theU-shaped recess being larger than the diameter of the rod; a one-piececlosure element configured to engage with said legs to simultaneouslyfix the rod in said recess of the pressure element and fix saidreceiving portion to the head; and wherein an inner thread is providedat said legs and said closure element is an inner screw and wherein,when the bone anchoring device is assembled, the closure element isscrewed-in between said legs and exerts a pressure directly on said rod,but not directly on said pressure element, to simultaneously fix the rodin said recess of the pressure element and fix said receiving portion tothe head.
 2. The bone anchoring element of claim 1, wherein said closureelement comprises a projection which contacts the rod.
 3. The boneanchoring device of claim 2, wherein the projection has a length that isselected such that there is a gap in the longitudinal direction betweenthe pressure element and the closure element when the rod is fixed. 4.The bone anchoring device of claim 1, wherein said closure elementcomprises a central projection acting on said rod, the length of thecentral projection being selected such that there is a gap between thepressure element and the closure element when the rod is fixed.
 5. Thebone anchoring device of claim 4, wherein a sum of the length of saidprojection and a diameter of the rod is greater than a height of thepressure element from the bottom of the recess of the pressure elementto the first end of the pressure element.
 6. The bone anchoring deviceof claim 1, wherein the inner thread ends above said rod when the rod isinserted in the recess of the pressure element, and wherein adjacent tothe inner thread, a guiding surface is provided for guiding theinsertion of the closure element.
 7. The bone anchoring device of claim1, wherein a maximum inner diameter of the receiving portion is notlarger than a diameter between opposing crests of said inner thread. 8.The bone anchoring device of claim 1, wherein said recess in thereceiving portion is substantially U-shaped.
 9. The bone anchoringdevice of claim 1, wherein said recess of said pressure element issubstantially U-shaped.
 10. The bone anchoring device of claim 1,wherein the inner thread opens out into the recess.
 11. A bone anchoringdevice comprising: an anchoring element comprising a shank to beanchored to a bone or a vertebra and a head; a rod; a receiving portioncomprising a first end and a second end opposite to the first end, alongitudinal axis passing through the two ends, a bore coaxial with thelongitudinal axis, a first region adjacent to the second end forreceiving said head and a recess which is opened towards the first endand which forms two free legs for receiving the rod; a pressure elementto exert a pressure on said head to lock said head in the receivingportion, wherein said pressure element has a first end and a second endopposite to the first end and a recess which is open towards the firstend to receive the rod, the depth of the recess being larger than thediameter of the rod; a one-piece closure element configured to engagewith said legs to simultaneously fix the rod in said recess of thepressure element and fix said receiving portion to the head; and whereinsaid closure element comprises a projection that, when assembled to thereceiving portion, extends into the recess of the pressure element andcontacts the rod to simultaneously fix the rod in said recess of thepressure element and fix said receiving portion to the head.